To be able to control the condition of a capacitor bank, it is normal to provide a protecting device, for example a tripping device, which is of a so-called balance type. This balance protection for a capacitor bank, divided into two parallel branches or sub-banks, is based on a comparison of the current in or the voltage across the two branches (sub-banks). A voltage or current difference exceeding a certain level indicates that a certain number of the capacitors are damaged, for example, through a short-circuit, which causes an alarm or tripping signal from the protection means. In the case of parallel capacitors, it is normal that they are series-connected with fuses to that the fuse for a short-circuited capacitor is released.
A condition for the release of a balance protection means, of this known kind, is that the damaged capacitors are located substantially in one of the branches or sub-banks. If, on the other hand, the capacitors are destroyed equally or nearly so, in the two branches, the voltage or current difference will remain below the tripping level of the protection means. In this fashion many capacitors may become damaged in the two branches to the point that the normal voltage of the bank destroys the remaining capacitors without the protection means ever tripping.